1. Field of the Invention
The present invention relates to a surface-mount type crystal oscillator, and particularly relates to a surface-mount type crystal oscillator capable of suppressing height from a wiring board to be low when surface-mounted on the wiring board.
2. Description of the Related Arts
Surface-mount type crystal oscillators each configured by integrating a quartz crystal blank and an IC chip which includes an oscillating circuit using the crystal blank are used as reference sources for frequency and time by being incorporated in portable electronic devices typified by, for example, portable telephones because of its compactness and light weight. Depending on the configurations of the devices in which the crystal oscillators are used, the surface-mount type crystal oscillators are sometimes required to be especially small in thickness, that is, height from the surfaces of the wiring boards, when they are surface-mounted on wiring boards of the devices. As the surface-mount type crystal oscillator which can be made small in height when surface-mounted, there is the one in which surface-mount type container with a recess formed on one principal surface is used, and a crystal blank and an IC chip are disposed in the recess side by side in the horizontal direction, as disclosed in Japanese Patent Laid-Open Application No. 9-83248 (JP-A-9-083248) and Japanese Patent Laid-Open Application No. 2006-13650 (JP-A-2006-013650).
FIG. 1A is a sectional view showing one example of a configuration of a conventional surface-mount type crystal oscillator configured to be reduced in height, and FIG. 1B is a plan view of this crystal oscillator with a cover removed.
In the illustrated surface-mount type crystal oscillator, crystal blank 2 and IC chip 3 are housed in a recess of container body 1, and crystal blank 2 and IC chip 3 are hermetically encapsulated in the recess by covering the recess with cover 4. Container body 1 is configured by laminated ceramics in which frame wall 1b with a substantially rectangular opening formed in a central portion is laminated on substantially rectangular bottom wall 1a. Accordingly, a planar shape of container body 1 is substantially rectangular, the recess is formed by the opening of frame wall 1b, and the surface of frame wall 1b is exposed on an inner bottom surface of the recess.
A pair of crystal holding terminals for use in electrical connection with crystal blank 2 and a plurality of circuit terminals for use in electrical connection to IC chip 3 are provided on the inner bottom surface of the recess. Mounting terminals 5 which are used when the crystal oscillator is surface-mounted on a wiring board are provided at four corner portions of an outer bottom surface of container body 1.
Crystal blank 2 is, for example, a substantially rectangular quartz crystal blank of AT-cut. Excitation electrodes 6 are respectively provided on both principal surfaces of crystal blank 2, and lead electrodes 7 are respectively extended from excitation electrodes 6 toward both sides of one end portion in the lengthwise direction of crystal blank 2. Crystal blank 2 is electrically and mechanically connected to the crystal holding terminals by fixing both sides of the one end portion where lead electrodes 7 are extended, onto the crystal holding terminals with conductive adhesive 8, and is horizontally held in the recess of container body 1.
IC chip 3 is in a substantially rectangular shape, in which electronic circuits such as an amplifying circuit which configures an oscillating circuit using crystal blank 2 are integrated on a semiconductor substrate. These electronic circuits are formed on one principal surface of the semiconductor substrate by an ordinary semiconductor fabrication process. Thus, out of both the principal surfaces of IC chip 3, the surface on which the electronic circuits are formed in the semiconductor substrate will be called a circuit formation plane. The circuit formation plane is provided with a plurality of IC terminals (not shown) for connecting the electronic circuits in IC chip 3 to external circuits. The IC terminals include, for example, a power supply terminal, a ground terminal, an oscillation output terminal, an AFC (automatic frequency control) terminal, and a pair of connection terminals which are electrically connected to crystal blank 2.
IC chip 3 is disposed on the inner bottom surface of the recess of container body 1 adjacently to and side by side with crystal blank 2 so that the circuit formation plane faces the inner bottom surface of the recess. For example, bumps 9 are provided on the IC terminals, and by the technique of flip-chip bonding through bumps 9, the IC terminals and the circuit terminals on the inner bottom surface of the recess are electrically and mechanically connected. Of the circuit terminals, the ones corresponding to the connection terminals of IC chip 3 are electrically connected to the crystal holding terminals via a wiring pattern (not shown) formed on the inner bottom surface of the recess of container body 1, whereby the oscillating circuit in IC chip 3 is electrically connected to crystal blank 2. Further, of the circuit terminals, the ones corresponding to the power supply terminal, the ground terminal, the oscillation output terminal and the AFC terminal of IC chip 3 are electrically connected to mounting terminals 5 through wiring paths (not shown) such as via holes formed in container body 1.
In the crystal oscillator, crystal blank 2 and IC chip 3 are disposed on the inner bottom surface of the recess of container body 1 side by side in the horizontal direction, and therefore, the dimension in the height direction of the crystal oscillator can be made small as compared with the one in which crystal blank 2 and IC chip 3 are disposed in the vertical direction, that is, the one in which crystal blank 2 is held above IC chip 3.
However, the surface-mount type crystal oscillator of the aforementioned configuration has the problem of being incapable of providing various communication terminals on an outer surface of the container body, though the height dimension can be made small. For example, when the crystal oscillator is configured as a temperature compensated crystal oscillator by providing the circuit of a temperature compensating mechanism, which compensates frequency temperature characteristics of the crystal blank, in IC chip 3, it is necessary to measure the actual frequency temperature characteristics of the crystal blank and write temperature compensation data based on the measurement result to the temperature compensating circuit before shipment of the crystal oscillator. Therefore, a write terminal for writing the temperature compensation data needs to be provided on the outer surface of the container body as a communication terminal. Further, when the vibration characteristic of crystal blank 2 in the state in which crystal blank 2 is hermetically encapsulated in container body 1 and fixed to the crystal holding terminals is desired to be inspected, and in order to conduct such inspection, a crystal inspection terminal electrically connected directly to crystal blank 2 needs to be provided on the outer surface of the container body as a communication terminal. These communication terminals are not used in an ordinary use state of the crystal oscillator after shipment.
It is conceivable to provide a communication terminal on an outer bottom surface of the container body, or provide a communication terminal in a depressed part by forming the depressed part on the outer bottom surface of the container body. However, when the communication terminal is provided like this, if the communication terminal is a crystal inspection terminal, the wiring pattern on the wiring board and the crystal inspection terminal are close to each other and both of them are electrically coupled, and may cause a change in oscillation frequency when the crystal oscillator is mounted on the wiring board.
In the crystal oscillator shown in FIGS. 1A and 1B, crystal blank 2 and IC chip 3 are housed in the same space formed in container body 1 and hermetically encapsulated. Therefore, when an abnormality of the vibration characteristic of the crystal blank is found in inspection after encapsulation, not only the crystal blank but also the IC chip has to be discarded, and productivity of the crystal oscillator is reduced correspondingly. Since IC chip 3 is also housed in the recess of container body 1, there is the problem that IC chip 3 needs to be small by the frame width of frame wall 1b configuring the recess as compared with the outside dimension of container body 1, and IC chip 3 of a large planar dimension cannot be used. Especially when the crystal oscillator is a temperature compensated crystal oscillator, IC chip 3 needs to contain a temperature compensation mechanism, and tends to have a large size as compared with a simple packaged crystal oscillator which is not of a temperature compensated type, and compactness of container body 1 is inhibited correspondingly.